The playback control technology above plays a very important role in realizing a media mix for sales—i.e. a single package where a digitized movie and a variety of applications are stored. Consider the case where one of the applications is, for example, a game-like program that uses characters appearing in the movie, and this application is executed simultaneously with a part of the digitized movie. This generates synergy effects between the video playback and the application execution, which will lead to the greater popularity of the movie.
The following patent reference 1 describes prior art of such playback control technology.    <Patent Reference 1> Japanese Patent Publication No. 2813245